The major long-term goal of the proposed selective breeding study is to shed light on an ubiquitous, easily assessed response to ethanol (hypothermia) that is useful as an index of sensitivity, tolerance and withdrawal from physical dependence on EtOH. We have been developing an animal model of genetic susceptibility to EtOH-induced HT. Using within-family selective breeding, lines and replicates have been selected for susceptibility (COLD) and resistance (HOT) to acute HT after 3 g/kg EtOH. The continued successful selection of the proposed lines could provide a much-needed genetic marker for predicting the susceptibility to develop ethanol physical dependence. The first goal of the proposed experiments is to continue to develop the HOT and COLD selected lines until response to selection has apparently reached its maximum. At this point, genes predisposing for alcohol sensitivity will presumably have been fixed in the homozygous state. The second goal is to determine genetic correlates of the HT response. A number of behavioral response to EtOH other than EtOH-induced HT, and hypothermic response to other agents postulated to share, or not to share, ethanol's mechanism of action will be compared in the HOT and COLD lines each 4 generations throughout selection. As a second method for verifying correlated response to selection, embryos from the lines will be frozen to preserve the genetic stock at regular intervals during the course of selection. The existence of cryopreserved embryos from each 4 generations of selection will allow subsequent testing for correlated responses to selection. In effect, a cross-sectional experiment can be done which recapitulates the developmental progress of the selection program. Cryopreservation will also provide an essential insurance policy against the possibility of loss of the COLD and HOT lines due to fire, infectious disease, "animal rights" activism, or other catastrophic loss. Additional stock of the lines will be bred and be made available for researchers who wish to perform mechanism-oriented experiments to elucidate the physiological and/or biochemical basis for alcoholism.